73 resultados para Catodo oco
Resumo:
"Counterinsurgency (COIN) requires an integrated military, political, and economic program best developed by teams that field both civilians and soldiers. These units should operate with some independence but under a coherent command. In Vietnam, after several false starts, the United States developed an effective unified organization, Civil Operations and Revolutionary Development Support (CORDS), to guide the counterinsurgency. CORDS had three components absent from our efforts in Afghanistan today: sufficient personnel (particularly civilian), numerous teams, and a single chain of command that united the separate COIN programs of the disparate American departments at the district, provincial, regional, and national levels. This paper focuses on the third issue and describes the benefits that unity of command at every level would bring to the American war in Afghanistan. The work begins with a brief introduction to counterinsurgency theory, using a population-centric model, and examines how this warfare challenges the United States. It traces the evolution of the Provincial Reconstruction Teams (PRTs) and the country team, describing problems at both levels. Similar efforts in Vietnam are compared, where persistent executive attention finally integrated the government's counterinsurgency campaign under the unified command of the CORDS program. The next section attributes the American tendency towards a segregated response to cultural differences between the primary departments, executive neglect, and societal concepts of war. The paper argues that, in its approach to COIN, the United States has forsaken the military concept of unity of command in favor of 'unity of effort' expressed in multiagency literature. The final sections describe how unified authority would improve our efforts in Afghanistan and propose a model for the future."--P. iii.
Resumo:
Esta dissertação apresenta um estudo da Revista O Cruzeiro tendo como f oco principal os gêneros jornalísticos praticados por essa publicação ao longo dos 47 anos em que pertenceu a Assis Chateaubriand/ Diários Associados. Com dois objetivos principais, procurou-se identificar, primeiramente, os gêneros, formatos e tipos de textos jornalísticos presentes na revista entre 1928 e 1975, além de definir as peculiaridades do jornalismo informativo do periódico. Por outro lado, procurou-se descobrir quais as principais temáticas abordadas pela mesma. Ambos os esforços foram realizados com o intuito de definir o perfil de O Cruzeiro. O trabalho foi pautado em duas metodologias, a primeira, Análise Formal que foi utilizada, sobretudo, na identificação dos gêneros a partir da Teoria dos Gêneros Jornalísticos. A segunda metodologia foi a Análise de Conteúdo por Construção Iterativa utilizada no momento da identificação das temáticas. Ao final conclui-se que O Cruzeiro era predominantemente uma revista Opinativa e que seu jornalismo Informativo diverge do praticado hoje, quanto ao modelo de construção da notícia. No que concerne aos assuntos jornalísticos tratados, vemos que os temas relacionados ao ambiente social predominavam inicialmente, tendo a política ganho destaque ao longo dos anos. Por outro lado, sua marca registrada, as grandes reportagens fotográficas realizadas com temas inéditos como candomblé e manicômios, dentre outros, dão a essa publicação um destaque no cenário brasileiro, contribuindo para que a mesma permaneça até os dias atuais como uma das melhores revistas de todos os tempos.
Resumo:
Group VI metal hexacarbonyls, M(CO)6 (M = Cr, Mo and W), are of extreme importance as catalysts in industry and also of fundamental interest due to the established charge transfer mechanism between the carbon monoxide and the metal. They condense to molecular solids at ambient conditions retaining the octahedral (Oh) symmetry of gas phase and have been extensively investigated by previous workers to understand their fundamental chemical bonding and possible industrial applications. However little is known about their behavior at high pressures which is the focus of this dissertation. Metal hexacarbonyls were subjected to high pressures in Diamond-Anvil cells to understand the pressure effect on chemical bonding using Raman scattering in situ. The high-pressure results on each of the three metal hexacarbonyls are presented and are followed by a critical analysis of the entire family. The Raman study was conducted at pressures up to 45 GPa and X-ray up to 58 GPa. This is followed by a discussion on infra red spectra in conjunction with Raman and X-ray analysis to provide a rationale for polymerization. Finally the probable synthesis of extremely reactive species under high-pressures and as identified via Raman is discussed. The high-pressure Raman scattering, up to 30 GPa, demonstrated the absence of Π-backbonding. The disappearance of parental Raman spectra for (M = Cr, Mo and W) at 29.6, 23.3 and 22.2 GPa respectively was attributed to the total collapse of the Oh symmetry. This collapse under high-pressure lead to metal-mediated polymeric phase characterized by Raman active δ(OCO) feature, originating from intermolecular vibrational coupling in the parent sample. Further increase in pressures up to 45 GPa, did not affect this feature. The pressure quenched Raman spectra, revealed various chemical groups non-characteristic of the parent sample and adsorption of CO in addition to the characteristic δ(OCO) feature. The thus recorded Raman, complemented with the far and mid-infrared pressure quenched spectra, reveal the formation of novel metal-mediated polymers. The X-ray diffraction on W(CO)6 up to 58 GPa revealed the generation of amorphous polymeric pattern which was retained back to ambient conditions.
Resumo:
Porous structures are being widely investigated for use in biomedical implants, aiming to mechanically integrate and functionally the implant inside the bone tissue. Moreover, this structure is also important for drugs that can be stored and can induce and accelerate the process of osseointegration. With the purpose to investigate this effect, Ti, Nb and Sn metal powders, were sintered by plasma using a hollow cathode discharge. Sintering was performed in argon plasma set at 4 mbar pressure and temperatures of 500 ° C, 600 ° C and 700 ° C. Samples were also sintered in the electrical resistance furnace at 1200 ° C in order to compare plasma sintering with the conventional method. It was observed that plasma samples sintered with the hollow cathode configuration showed a gradient in porosity, while the samples sintered in the resistive furnace did not. Furthermore, differences in the microstructure of the samples were found, were a surface with higher porosity and ales porous core were obtained at different temperatures. The percolation profile of distilled water and the chemical compositions of the porous layers of the plasma treated samples were the main results obtained. Based on these results, we can conclude that this structure is particularly important for application in the biomedical field such as scaffolds for drug delivery and implants
Resumo:
This work was performing effluent degradation studies by electrochemical treatment. The electrochemical oxidation (EO) hydroquinone (H2Q) was carried out in acid medium, using PbO2 electrode by galvanostatic electrolysis, applying current densities of 10 and 30 mA/cm2 . The concentration of H2Q was monitored by differential pulse voltammetry (DPV). The experimental results showed that the galvanostatic electrolysis process performance significantly depends on the applied current density, achieving removal efficiencies of 100% and 80 % and 10 applying 30 mA/cm2 , respectively. Furthermore, the electroanalytical technique was effective in H2Q be used as a detection method. In order to test the efficiency of PbO2 electrode, the electrochemical treatment was conducted in an actual effluent, leachate from a landfill. The liquid waste leachate (600ml effluent) was treated in a batch electrochemical cell, with or without addition of NaCl by applying 7 mA/cm2 . The efficiency of EO was assessed against the removal of thermo-tolerant coliforms, total organic carbon (TOC), total phosphorus and metals (copper, cobalt, chromium, iron and nickel). These results showed that efficient removal of coliforms was obtained (100%), and was further decrease the concentration of heavy metals by the cathode processes. However, results were not satisfactory TOC, achieving low total removal of dissolved organic load. Because it is considered an effluent complex were developed other tests with this effluent to monitor a larger number of decontamination parameters (Turbidity, Total Solids, Color, Conductivity, Total Organic Carbon (TOC) and metals (barium, chromium, lithium, manganese and Zinc), comparing the efficiency of this type of electrochemical treatment (EO or electrocoagulation) using a flow cell. In this assay was compared to electro streaming. In the case of the OE, Ti/IrO2-TaO5 was used as the anode, however, the electrocoagulation process, aluminum electrodes were used; applying current densities of 10, 20 and 30 mA/cm2 in the presence and absence of NaCl as an electrolyte. The results showed that EO using Ti/IrO2–TaO5 was anode as efficient when Cl- was present in the effluent. In contrast, the electrocoagulation flow reduces the dissolved organic matter in the effluent, under certain experimental conditions.
Resumo:
La seguente tesi prevede la costruzione e caratterizzazione di un micro-supercapacitore asimmetrico composto da un anodo a base di ZnO ed un catodo a base di grafene ossido ridotto (rGO); la combinazione di due materiali con differente natura di accumulo di carica permette quindi di ottenere dispositivi con migliori performance elettrochimiche. Entrambi gli elettrodi sono stati depositati per via elettrochimica su substrati flessibili di PET-ITO. L'ottimizzazione delle proprietà dello ZnO è stata fatta tramite l'aggiunta di molecole di tensioattivi durante la deposizione dello stesso. I risultati ottenuti mostrano un effettivo miglioramento delle proprietà elettrochimiche e della trasparenza dei film di ZnO prodotto grazie all'effetto di tali tensioattivi. Inoltre anche le proprietà di rGO sono state ottimizzate allo scopo di ottenere buone proprietà elettrochimiche abbinate all'elevata trasparenza del film prodotto. Infine sono stati costruiti micro-supercapacitori allo stato semisolido con differenti agenti gelificanti (silice e Nanoclay) ed il loro funzionamento è stato dimostrato.
Resumo:
The work presents the effect of plasma treatment when applied in fibers or carbon/glass posts in the adhesion fiber/resin and posts/cement. This has for objective the modification of the surface of the fibers, as well as the wettability of the posts, seeking the improvement of the adhesion and of the connection fiber/resin in the processing of polymeric composites reinforced with the same ones. 120 posts (Reforpost) were used and 30 meters of fibers of carbon and of glass (Fibrex), of the company Angelus. The samples were divided in three groups of 40 specimens: GROUP I - 20 posts of glass fiber and 20 of carbon without treatment to it shapes, GROUP II -20 posts of glass fiber and 20 of carbon treated to it shapes in the surface and GROUP III - 20 posts of glass fiber and 20 of carbon make with fibers in natura after plasma treatment. The plasma treatment was accomplished with oxygen and with temperature in the camera fixed at 200°C, for one hour of exhibition. The posts and the fibers were characterized before and after the treatment. The wettability was measure by pendent drop method, and interface fiber/resin and posts/cement were observed by optical and electronic microscopy. It was observed that both wettability and texture were increased with plasma treatment
Resumo:
The ionic plasma nitriding is one of the most important plasma assisted treatment technique for surface modification, but it presents some inherent problems mainly in nitriding pieces with complex geometries. In the last four years has appeared a plasma nitriding technique, named ASPN (Active Screen Plasma Nitriding) in which the samples and the workload are surrounded by a metal screen on which the cathodic potential is applied. This new technique makes possible to obtain a perfect uniform nitrided layer apart from the shape of the samples. The present work is based on the development of a new nitriding plasma technique named CCPN (Cathodic Cage Plasma Nitriding) Patent PI 0603213-3 derived from ASPN, but utilizes the hollow cathode effect to increase the nitriding process efficiency. That technique has shown great improvement on the treatment of several types of steels under different process conditions, producing thicker and harder layers when compared with both, ASPN and ionic plasma nitriding, besides eliminating problems associated with the later technique. The best obtained results are due to the hollow cathode effect on the cage holes. Moreover, characteristic problems of ionic plasma nitriding are eliminated due to the fact that the luminescent discharge acts on the cage wall instead of on the samples surface, which remains under a floating potential. In this work the enhancement of the cathodic cage nitriding layers proprieties, under several conditions for some types of steels was investigated, besides the mechanism for nitrides deposition on glass substrate, concluding that the CCPN is both a diffusion and a deposition process at the same time
Resumo:
Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500°C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3μm and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 °C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar α of the components of a SOFC and had presented steady crystalline phases
Resumo:
The present work deals with the synthesis of materials with perovskite structure with the intention of using them as cathodes in fuel cells SOFC type. The perovskite type materials were obtained by chemical synthesis method, using gelatin as the substituent of citric acid and ethylene glycol, and polymerizing acting as chelating agent. The materials were characterized by X-ray diffraction, thermal analysis, spectroscopy Fourier transform infrared, scanning electron microscopy with EDS, surface area determination by the BET method and Term Reduction Program, TPR. The compounds were also characterized by electrical conductivity for the purpose of observing the possible application of this material as a cathode for fuel cells, solid oxide SOFC. The method using gelatin and polymerizing chelating agent for the preparation of materials with the perovskite structure allows the synthesis of crystalline materials and homogeneous. The results demonstrate that the route adopted to obtain materials were effective. The distorted perovskite structure have obtained the type orthorhombic and rhombohedral; important for fuel cell cathodes. The presentation material properties required of a candidate cathode materials for fuel cells. XRD analysis contacted by the distortion of the structures of the synthesized materials. The analyzes show that the electrical conductivity obtained materials have the potential to act as a cell to the cathode of solid oxide fuel, allowing to infer an order of values for the electrical conductivities of perovskites where LaFeO3 < LaNiO3 < LaNi0,5Fe0,5O3. It can be concluded that the activity of these perovskites is due to the presence of structural defects generated that depend on the method of synthesis and the subsequent heat treatment
Resumo:
The ionic nitriding process presents some limitations related with the control of the thickness of the layer and its uniformity. Those limitations that happen during the process, are produced due to edge effects, damage caused by arcing arc and hollow cathode, mainly in pieces with complex geometry and under pressures in excess of 1 mbar. A new technique, denominated ASPN (active screen shapes nitriding) it has been used as alternative, for offering many advantages with respect to dc plasma conventional. The developed system presents a configuration in that the samples treated are surrounded by a large metal screen at high voltage cathodic potencials, (varying between 0 and 1200V) and currents up to 1 A. The sample is placed in floting potential or polarized at relatively lower bias voltages by an auxiliary source. As the plasma is not formed directly in the sample surface but in the metal screen, the mentioned effects are eliminated. This mechanism allows investigate ion of the transfer of nitrogen to the substrate. Optical and electronic microscopy are used to exam morphology and structure at the layer. X-ray difration for phase identification and microhardness to evaluate the efficiency of this process with respect to dc conventional nitriding
Resumo:
Alternative and clean energy generation research has been intensified in last decades. Among the alternatives, fuel cells are one of the most important. There are different types of fuel cells, among which stands out intermediate temperature solid oxide fuel cell (IT-SOFC) matter of the present work. For application as cathode on this type of devices, the ceramic Ba0.5Sr0.5C0.8Fe0.2O3-δ doped with rare earth ions (Nd, Sm) have been quite promising because they show good ionic conductivity and operate at relatively low temperatures (500 - 800°C). In this work, Ba0.5Sr0.5Co0.8Fe0.2O3-δ, (BaSr)0.5Sm0.5Co0.8Fe0.2O3-δ and (BaSr)0.5Nd0.5C0.8Fe0.2O3-δ were obtained by modified Pechini method, making use of gelatin as polymerizing agent. The powders were characterized by X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). The perovskite phase was observed in all X-ray patterns for the materials Ba0.5Sr0.5C0.8Fe0.2O3-δ doped with rare earth ions (Nd, Sm). The SEM images showed that the materials have a characteristics porous, with very uniform pore distribution, which are favorable for application as cathodes. Subsequently, screen-printed assymmetrical cells were studied by impedance spectroscopy, to assess the kinetics of the cathode for the reduction reaction of oxygen. The best resistance to the specific area was found for the cathode BSSCF sintered at 1050 °C for 4 hours with around 0.15 Ω.cm2 at 750 °C as well as cathodes BSNCF and BSCF obtained resistances specific area of 0.2 and 0.73 Ω.cm2, respectively, for the same conditions. The polarization curves showed similar behavior to the best cathodes BSSCF and BSNCF, such combination of properties indicates that the film potentially depict good performance as IT-SOFC cathodes
Resumo:
The heat transfer between plasma and a solid occurs mostly due the radiation and the collision of the particles on the material surface, heating the material from the surface to the bulk. The thermal gradient inside the sample depends of the rate of particles collisions and thermal conductivity of the solid. In order to study that effect, samples of AISI M35 steel, with 9,5 mm X 3,0 mm (diameter X thickness) were quenched in resistive furnace and tempereds in plasma using the plane configuration and hollow cathode, working with pressures of 4 and 10 mbar respectively. Analyzing the samples microstructure and measuring the hardness along the transversal profile, it was possible to associate the tempered temperature evaluating indirectly the thermal profile. This relation was obtained by microstructural analyzes and through the hardness curve x tempered sample temperature in resistive furnace, using temperatures of 500, 550, 600, 650 and 700°C. The microstructural characterization of the samples was obtained by the scanning electron microscopy, optic microscopy and X-ray diffraction. It was verified that all samples treated in plasma presented a superficial layer, denominated affected shelling zone, wich was not present in the samples treated in resistive furnace. Moreover, the samples that presented larger thermal gradient were treated in hollow cathode with pressure of 4 mbar